E34 540 de-cat

[Sidney Rough-Diamond]

Here in the UK I could *maybe* get away without running any cats on my car. So is it worth it bearing in mind I track the car and what power gain could I expect. I did also note that the cat section also seems to sell for good money,so this could fund a custom de-cat section to mate with the orginal back section of the exhaust. Your thoughts please.

[Sam-Son]

you could always just hollow out the cat

[repenttokyo]

i would think the power gains would be minimal.

[Rocky454]

i would think the power gains would be minimal.

Why would the gains be minimal when you're decreasing resistance?

[DaveVoorhis]

Why would the gains be minimal when you're decreasing resistance?
The resistance caused by the cat is negligible relative to the power of the engine. With just a hollowed-out cat, you probably wouldn't notice the difference.

[repenttokyo]

Why would the gains be minimal when you're decreasing resistance?


because these engines aren't powerful enough to respond to such a small amount of resistance being removed. Also, exhaust systems aren't just about less resistance = more power...

[Alexlind123]

because these engines aren't powerful enough to respond to such a small amount of resistance being removed. Also, exhaust systems aren't just about less resistance = more power...

Well, its not really because these engines arent powerful enough. A small increase in power would be noticeable because of that. I think its mainly because BMW designed the exhaust adequately, at least compared to the vast majority of cars on the road.

[repenttokyo]

Well, its not really because these engines arent powerful enough. A small increase in power would be noticeable because of that. I think its mainly because BMW designed the exhaust adequately, at least compared to the vast majority of cars on the road.


I don't feel removing high flow cats on any application under 500 hp pushes enough exhaust gasses to see a beneficial flow improvement leading to a useable amount of hp being created. It is precisely because these are high flow cats that this is the case.

One exception would be on a forced induction platform, but even still, under 500, I don't see the benefit. It's not like you are removing a major restriction.

[Ferret]

Quick thought though - the new digitised MOT systems will demand your reg no/chassis no etc - it /knows/ if you're supposed to have a cat or not.

I'd double check with a garage first, and see what happens.

Surely the bmw cats are large enough that it wont really matter?

[Stephan735i]

It's much better to change rear Muffler to a sport silencer because that's what's stops the flow, the cats were designed to the engine, change to sportcats the helps but just to take them off, gives you nothing at best, at worst the car gets slower.

Regards Stephan

[bmw540]

Suggest replacing the standard cats with high flow metal core cats. Do not run ceramic otherwise you will be doing this again after a couple of months.

I have found Magnaflow 2 1/2 inch metal cats in aus for $200 each.

You will get alittle more performance which I have also noticed The exhaust note is also alot better.